Oxyallyl cations, as powerful electrophilic intermediates, have shown versatile utilities in organic synthesis. Modular synthesis of multi‐substituted cyclobutanones enabled by oxyallyl cations provides facile access to multi‐substituted cyclobutanones via direct nucleophilic substitution of (di)chlorocyclobutanones under mild basic conditions. Both aryl or alkyl substituents could be efficiently introduced on the four‐membered ring skeleton. Further transformation leads to tetrasubstituted cyclobutane derivatives in a stereoselective manner, demonstrating potential synthetic utility. More details are discussed in the article by Lu et al. on page 459—463.image